you vastly underestimate civilians. probably not a single gun is needed. a crowd of people at some point will walk into the billionaire's home and make him agree with handing over his wealth. They might call the police, but all thats needed is the officers ignoring the call willingly. Why should they defend those billionaires? What should they do? Rich people depend on many individual poor laborers, all of them can simply decide to no longer accept his state of affairs and there is lietrally nothing the billionaires could do against it.

Ideally, defund the police and so on, so that every state worker also is keen on getting that wealth redistribution done.